I purchased this lens recently by itself. I am extremely satisfied with the image quality but i have a question about filters. I always buy a clear filter for lens protection. The man who sold me the lens said i have to buy a 70-80 dollar filter because the cheap ones ruin the good quality of the lens. I did not buy one because i think 80 dollars is a crazy price for a clear filter. Do i really have to buy such a expensive filter or will a 30-40 dollar one do? Does it really affect photo quality? Is it something i should get or no?